1. Field of the Invention
The present invention relates to a liquid discharge head that performs a recording operation by discharging a liquid such as ink to a recorded medium such as recording paper and a method for manufacturing the liquid discharge head.
2. Description of the Related Art
In a conventional liquid discharge head, bump bonding or wire bonding to a tape automated bonding (TAB) film is used in an electric connection technique between a recording element substrate and an electric wiring board such as a flexible wiring board. Further, a full-line type liquid discharge head including a liquid discharge head having a width comparable to a print width is known as a form of the liquid discharge head.
The flexible wiring board applied to a full-line type liquid discharge head is used to apply an electric signal for discharging ink to the recording element substrate from outside. The flexible wiring board includes an electrode terminal corresponding to an electrode of the recording element substrate and an external signal input terminal positioned at a wiring edge to receive an electric signal from a recording apparatus body. The flexible wiring board and the recording element substrate are electrically connected by a wire bonding technique using a gold wire or the like. The electrode of the recording element substrate, the electrode terminal of the flexible wiring board, and the gold wire are sealed by a sealing agent and protected from corrosion by ink or an external impact.
Ball bonding is commonly used as the wire bonding technique. The shape of a wire after wire bonding is generally a mountain shape in which the wire rises up from a wire start-edge and passes a bending point before reaching a wire end-edge. In recent years, however, various low-loop formation techniques have been developed to suppress the height of a wire, leading to diversification of wire shapes.
Poor conduction or a defective shape that occurs after the wire bonding in common wire bonding connection is handled as a failure in the manufacturing process of ink jet heads. For a full-line type liquid discharge head in which a plurality of recording element substrates is arranged, however, many recording element substrates are mounted and the number of wires to be connected increases, so that the probability that poor connection in wire bonding occurs may increase. Thus, a manufacturing yield of liquid discharge heads may be lowered, and manufacturing costs may increase. Japanese Patent Application Laid-Open No. 08-187860 discusses a configuration in which a plurality of wires is stacked and connected to an electric connection portion connected by a wire to reduce failures due to wire bonding. If the configuration is used, even if an out-of-spec wire causing poor conduction is found by a test after wire bonding, connection can be established by another wire connected to the same connection portion, so that the manufacturing yield of the liquid discharge head can be prevented from decreasing due to a defective wire.
However, the following issue is found to occur if this configuration is applied to an ink jet head. More specifically, according to the configuration discussed in Japanese Patent Application Laid-Open No. 08-187860, a plurality of wires with different heights is connected to the same connection portion. Thus, the height of wires formed in the end increases according to the number of wires connected to the same connection portion and therefore, even if the low-loop formation technique is used, the height of the wire located at the highest position will be relatively high.
One effective element to improve print quality in an ink jet recording apparatus is to make a head-to-paper distance smaller. The head-to-paper distance is an interval between a discharge port surface on which a discharge port for discharging ink droplets is formed and recording paper that receives discharged ink droplets. If the head-to-paper distance is large, deterioration in the print quality is caused by lower precision with which ink dots are impacted onto the recording paper or deformed dot shapes. One cause of the increasing head-to-paper distance is the height of wires of wire bonding and the sealing agent covering the wires. The height of the sealing agent is almost the same as the height of wire and thus, making the wire height of wire bonding as low as possible is effective in making the head-to-paper distance smaller.